Mechanisms of alamethicin ion channel inhibition by amiloride in zwitterionic tethered lipid bilayers

Abstract

The effect of amiloride, an acid-sensing ion channel (ASIC) blocker, on the formation of alamethicin ion channels in tethered zwitterionic phospholipid bilayers was investigated using electrochemical impedance spectroscopy (EIS) and polarization modulation infrared reflection absorption spectroscopy (PM-IRRAS). EIS measurements show a decrease in conductivity indicating that ion transported across the alamethicin-rich phospholipid membrane is inhibited by the presence of amiloride. The PM-IRRAS spectra indicate that amiloride has no effect on the secondary structure of the alamethicin peptide. The IR data suggests that amiloride does not block ion translocation through the alamethicin ion pore but prevents the insertion of alamethicin peptides into the biomembrane suppressing the formation of ion channels. The mechanism responsible for amiloride inhibition is explained in terms of the electrostatic interactions between the molecule and membrane surface. Amiloride is positively charged at physiological pH levels invoking a repulsive force on the positive pole of the alamethicin molecular dipole. These repulsive interactions prevent the insertion of the alamethicin peptides into the hydrophobic core of the lipid bilayer. The present paper offers a molecular view of the interactions that occur between amiloride, an ion channel inhibitor, with the lipids and ion channel forming peptides in model tBLMs.